A marine engine system may include a number of components such as, for example, an engine with one or more combustion chambers, a power output unit including a transmission and a propeller, a coolant passage, and a cooling system. Some components of a marine engine system may have direct contact with fluids, such as water. For example, the engine cooling system may use untreated raw water to reduce engine temperature. Some engine system components may be made of metal materials (e.g., steel, aluminum, etc.), which may be sensitive to corrosion by water, such as sea water. Corrosion may cause damage and/or failure of system components, and may result in the lost time and the expense needed to repair or replace the corroded components.
A number of corrosion protection techniques and procedures have been developed. For example, anti-corrosive coating can be applied to the surface of metal components directly exposed to raw water, such as sea water. Although this technique may provide some protection, the protective coating may be damaged and may require regular maintenance, including replacing the damaged coating. Another technique is galvanic cathodic protection, which employs a sacrificial anode made of a metal with higher potential (e.g., zinc or magnesium) than that of the metal (cathode) being protected (e.g., steel or copper). While the galvanic cathodic protection technique may provide effective protection to a marine engine system, it usually requires regular replacement of the sacrificial anode metal due to its gradual consumption. Another technique is impressed current corrosion protection, which uses anode and cathode elements as in the galvanic protection technique, but generates an electric current for delivery to the anode element from an external power source, for example, a battery. In this technique, the anode is not sacrificially consumed.
An impressed current corrosion protection system for a marine engine is disclosed in U.S. Patent Application Publication No. 2006/0213765 A1 to Mizuno et al. (“the '765 publication”). In the system of the '765 publication, a plurality of electrically insulated electrodes are disposed in a coolant passage of an engine filled with conductive coolant. With electrodes connected to an external power supply device, a protective current is generated between the electrodes, transmitted through the conductive coolant, and controlled by a controller for corrosion protection.
While the system of the '765 publication may control corrosion of an engine coolant passage, the system relies on a constant voltage supply or a constant current supply to the electrodes. The constant voltage or current level generated by the controller might be adequate for corrosion protection when initially set up under a certain environment, but may no longer be adequate in a changing environment. As a result, system components may be insufficiently protected against corrosion.
The disclosed corrosion protection system is directed toward improvements and advancements over the foregoing technology.